The present invention relates to pressure sensitive adhesive materials, more particularly to pressure sensitive adhesive linerless labels.
Typical linerless labels are disclosed in U.S. Pat. Nos. 5,292,713 and 4,978,415, and copending applications Ser. Nos. 07/912,851 filed Jul. 13, 1992, 07/907,511 filed Jul. 1, 1992, 07/982,699 filed Nov. 30, 1992, and 08/078,918 filed Jun. 2, 1993, the disclosures of which are each hereby incorporated by reference herein.
Linerless label constructions are typically manufactured by applying a permanent, removable or repositionable pressure sensitive adhesive onto one side of a paper or synthetic continuous substrate or web and applying a release coating to the opposite side of the substrate. The resultant article is then wound upon itself to form a roll. The presence of a release coating on the side of the substrate opposite the adhesive allows the article to be rolled up and then subsequently unrolled, without the adhesive sticking to the substrate. The adhesive sticking to the substrate can prevent the substrate from unrolling. Linerless labels obviate the need for a separate release sheet or liner that must be stripped from the adhesive layer and discarded prior to applying the adhesive substrate to the intended surface. Such liners are inconvenient and often constitute an environmental problem.
However, linerless labels known in the art suffer from several disadvantages. For example, for many applications, it is desirable to print variable indicia on the side of the substrate opposite the adhesive, by means such as ink jet, thermal transfer, flexographic or lithographic. Such applications include for example, shipping, warehouse, and inventory forms and related industrial application forms. But, the presence of a release coating on the side of the substrate opposite the adhesive hinders the ability to apply printed material to the substrate. The surface energy of the release coating prevents wax based toners, inks, and coatings from adhering. Presently, most inks, including ribbon based inks, toners, and coatings, are wax based. The release face of a linerless label has little or no porosity to allow either ink to absorb or toner to become anchored. With conventional linerless labels, the printing can be wiped off or smeared upon contact with other surfaces. Thus, such a product is not compatible with impact or non-impact printers.
Additionally, prior art labels suffer from the disadvantage that the release coating, which is usually glossy in appearance, interferes with bar code scanners.
The prior art has used various materials to overcoat an adhesive layer to deaden or destroy the tackiness properties of the adhesive. The adhesive property is not masked but rather is rendered non-tacky until the adhesive is reactivated by, for example, solvent or water. The use of solvent in the workplace creates hazards such as fumes, which must be vented, and flammability and disposal problems. With water soluble blockers, long term storage, prolonged handling, and exposure to the elements create additional care concerns. Furthermore, the user of the water reactivated label must apply water by manual or other means directly to the label substrate prior to using. This is a messy and time consuming operation. The application of water soaked labels leads to dripping in the area of application creating additional work hazards from the accumulation of moisture on the floor.